Water-laid fibrous sheets



WATER-LAID FIBROUS SHEETS Jay -L. Piersol, East Hempfield Township, Lancaster County,1 Pa., assignor to Armstrong Cork Company, Lancaster, Pa., a corporation ofPennsylvania No Drawing. Filed Nov. 12, 1957, Ser. No. 695,520 9 Claims. Cl. 162-169) i Add paper I maker's alum Add ammonium hydroxide Add finely divided zinc oxide I Add ,i synthetic rubber latex Form sheet I l f I In US. Patent 2,375,245--Pretzel, issued May 8, 1945, there is described a' process of controlling the deposition of a synthetic rubber binder onto cellulosic fibers. The process contemplates pretreating the fibers with a watersoluble'salt of aluminum, magnesium, or zinc, followed by the addition of ammonium hydroxide to form the insoluble metallic hydroxide. The subsequent addition of a synthetic rubber latex brings about the smooth and even deposition of the rubber particles on the individual fibers in the slurry. The rubber coated :furnish fiber; stock is then fed to a paper-forming machine such as a Fourdrin ier, cylinder machine, or the like. This process allows 2,971,879 Patented F eb, 14, 1961 excellent control of the deposition of rubber on fibers in a papermaking slurry.

However, it has been found that aluminum hydroxide, because of its highly gelatinous nature, is a dispersing agent as Well as a precipitating agent for rubber latices under the conditons described in the Pretzel process. The result of this situation is that a slow-draining stock sometimes results from use of the Pretzel process, particularly where higher amounts of aluminum hydroxide are formed in the slurry. Thus there is often a need for a modification of the Pretzel process which will produce a faster draining stock.

It is the primary object of the present invention to supply such a modification. It is a further object of the present invention to produce a papermaking furnish prepared by the Pretzel process which has a higher Canadian freeness than would normally be expected.

These objects are accomplished in a surprisingly straightforward and eflfective manner. The invention contemplates the addition of finely divided zinc oxide subsequent to the step of adding the ammonium hydroxide to form the metal hydroxide in the Pretzel process and prior to the step of adding the'synthetic rubber latex. The result of the addition of zinc oxide at this point in the Pretzel process is that the stock possesses a higher Canadian freeness, presents a more clumpy appearance to the eye, and enables the formation of a thicker sheet.

The fibers contemplated for treatment by the present invention are cellulosic fibers such as kraft, rags, soda. pulp, wood pulp, cotton linters, and the like. The fibers may be present in the slurry along with additional, sheetforming materials such as finely divided cork or finely divided scrap foam rubber; use of finely divided cork with fibers is fully described in US. Patent 2,613,190Feigley. The fibers and additional material, if any, aretaken up in water in the usual manner to form a slurry which will generally be in the consistency range of about 0.5-5%. This slurry may then be subjected to mechanical refining in the usual refiners such as Jordan engines, beaters, disc refiners, and the like. When the desired degree of refinement has been achieved, the consistency-may be adjusted to that desired for further treatment. Generally this consistency will be in the range of about l3%.

To the slurry there is then added a water-soluble salt of a suitable electrolyte such as papermakers alum, aluminum chloride, aluminum sulphate, magnesium chloride, magnesium sulphate, zinc chloride, and the like. For convenience the salt may be added in the form of its water solution. The amount of the electrolyte to be added will generally be in the range of about 25-75% I by weight based on the amount of rubber to be deposited on the fibers subsequently. 1

After the electrolyte has been added to the slurryfand dissolved therein, sufficient ammonium hydroxide is added to establish a substantially neutral pH. To state it another way, sutficient ammonium hydroxide is added to react with and form the hydroxide of substantially all of the metal ion present in the aqueous phase of the slurry.

The reaction proceeds rapidly, and gentle agitation for-' a few minutes is all that is needed.

Instead of adding next the synthetic rubberlatex as contemplated by the Pretzel process, the presentinvention calls for the addition of zinc water; the slurry is simply poured into the papermaking slurry with gentle agitation. The zinc oxide is added as finely divided zinc oxide commonly known as pigment grade or filler grade zinc oxide; these are readily available incommerce. The amount of zinc oxide to be added 1 of aluminum hydroxide which has been formed in the papermaking slurry. Since will be controlled by the amount the amount of aluminum hydroxide is controlled to some oxide at this point. The zinc oxide is preferably added in the form of a slurryin- :acrnere r extent by the amount of rubber to be "deposited on "ihe fibers, it can be seen that the amount of rubber ultimately controls the amount of zinc oxide to be added. Generally speaking, the zinc oxide will be added in an amount of about 3-50% j by" weight based on the total weight of rubber to be deposited on the fibers.

Upon the addition of'zinc oxide to the paperrnaking slurry, some of thelinc oxide apparently immediatelyde positson the aluminum hydroxide-treated-fibersand some stays suspended in the water phase of thepaper-making slurry. Once the zinc oxide has been thoroughly dispersed throughout thepaperrnaking-slurry, the synthetic rubber latex may be added. V

V The synthetic rubber latices contemplated for, use in thepre sent invention'arejthose latices widely media the beater saturation processes. Typical of these synthetic rubbers arethe products *known as; GR+S, which is a copolymer of butadiene and-styrene containing about 50% to about 70% butadiene. There may also be used those products known ,as l lycars, which are copolymers of'butadiene-and acrylonitrile containing about 50% to about 80% butadiene. The polychloroprenes may also be'used. The polychloroprenes, often called neoprenes,

at'aaia 'Eiheto ihe "zinc bate seamen. we

pared according to the progess of the present invention find use as a backing for linoleum composition and plastic surface coverings. Additionally, gaskets may be cut from the sheets, which gaskets find wide use in the automotive and airplane industries.

The following examples illustrate several embodiments of the invention. All parts are' by weight unless otherwise stated.

Example 1 mm 3,750 parts of water there was asse-1" kraft fiber, and 20 parts "Of finelydi'vide'd foam rubber scrap. There was then added 10 -parts papermakers are polymers'of-Z-chlordbutadiene-1,3. If desired homop'olyin'erso'f 'butadiene may begemployed as well as homopolymers and/or copolymers of butadiene homologues snchasisoprene. T hese materials can be vgenerally designated as "synthetic rubbers and more specifically designated asrubberlike polymers of butadiene, isoprene,

and chlorop're ne, and rubberlike copolymers of butadiene or isoprene with copolynierizable vinyl compoundssuch as styrene and acrylonitrile. As is well known in beater saturation 'niethodsgthe'sesynthetic rubbers are added to the slurry in the form of a :latex. The rubber particles therein constitutean electrone gatively charged organic binding material. ,These latices normally contain about 25 to about 50% by weight solids and'contain additional compounding ingredients such as stabilizers and thelike which'arewell known to the art and which {form no part of this invention. The latices are added in an amount suflicie'nt 'to introduce the required amount of r'ubberto be deposited on the fib ers. Normally this will bein'the range; of about 10-1 00% iby weight rubber based on the dry Weight of'the fiber s. v V U V I Theselected latexis simplypoured into the zinc oxide treated slurry withgentle agitation. Therubber content or the latex coagulats and evenly deposits upon the fibers. Since'zinc oxide is subst'antiallyiinsoluble in water under the beater saturation conditions of the Pretzel process, the rubber particles carry with-them all the zinc-oxide which is suspended in the whitewater. The resulting coatedfibers carrfyaninner coating of Zinc oxide and an outer'coating'of a synthetic rubber binder, which binder distributed throughout additional particles of zinc 0x1 e.

Agitation is maintaineduntil rubber precipitation is complete. Normally the necessary period oftime runs less than 20 minutes and often less than 10 minutes. Complete'preci'pitation'is indicated by the fact that the water phaseof thepapermaking'slurry is water white and alum dissolved in 100 parts 'of water, with gentle agitation. There was then added "8' parts aimrhonium hydroxide (28%) with continuing agitation.

A butadiene-styrene latex containing styrene, 40% by weight solids (FRS-ZOOO was added to the resulting slurry in anamount of 45 parts. 7 Antioxidantstofstabilize the rubber against oxidation were "also added, ifria 1.34 partsof a 45% dispersion ofainixtureoff I and 'di-heptyl'diphenyl amines, and 0,75 part .poly merized l,2-dihydro'-2,2,4-trimethyl quinolijne. 'rreeipi: tation of the rubber was 'complete'in 5 minutes,

A slurry identical to that described jjabove pared save for the addition of ninc'oxidesubs n the addition of the ammonium hydroxide and pribrto the addition, of the synthetic rubber --latex. The zinc oxide was addedin the form of a 48% dispersionin' waten and 1.56 parts of the dispersion was added. M m V The Canadian f r'eeriess of the stock containing no zinc oxide was 650 and the stock was only very slightly clumpy. The Canadian 'fre'eness Gfthe stock containing the zinc oxide was 750 an}; fthe stock had a definite clumpy appearance to 'HE eye;

Sheets were prepared fromboth stocks in a 12" x 12" laboratory mold and werefsubse'cfintly dried in an aircirculating oven maintained at "195 F. The zinc oxide treated stock drained faster and allowed the production of a thicker sheet than did the stock not treated with zinc oxide.

Example Two slurries were prepared having'the ingredients listed below. The various ingredients were added in the order given.

Ingredients Run 1, Run 2,

7 parts parts Kraft Fibers 7. 5 7.5 Cotton Linters 7. 5 7. 5 Aluminum Sulphate"--. 6. 5 6.5 NHrOH, 23% 5 6 Zinc Oxide 1 5.8 Butariiene-Styrene Copolymer Latex, 50%

Styrene, 40% Solids 22. 5 22. 5

Canadian Freeness 530 760 clear containing jno suspended particles either o=rubber or zinc oxide; The slurry itself "will possess 'a more clumpy appearantx': to the eye than an identical slurry prepared without the use of. zinc oxide. The Canadian freeness .of the zinc oxide treated slurry will .be higher than an identical slurry not treated with 'zinc'oxide.

"The specificity 'o'f zihc oxide as a means of improving drainage rate is unexpected and surprising. Aseries of similar compounds gives no improvement whatsoever. Zinc oxide appears to stand alone in this respect, the

reasons for which are not understood.

The completed slurryi's next form ed into a sh eet 'on the usual papermaking machine such as -a Fourdrinier wire, cylinder machine, or the like. The resulting sheet on the wire, especially in heavier gauges, will befaster (65% dispersion in water.) v The slurry prepared in -run 1 was smooth while the slurry prepared in run 2 was very-clumpy. 60

nesium oxide, zinc sulphide, iron foxi'de '(1=e, or), f miumoxide (Q 0 1,and'zinc'sulphate. lfloch'ange;was,

noted in the drainage rate or clumpiness "of'fthe "final slurry. 1 I

I claim: 7 1. -In the process or producing" by suspending fibers ma-salaries containing thedis solveiif salt of the metal of the group consisting of aluminum, magnesium, and zinc, mixing with said solution and the fibers suspended therein an aqueous solution of am monium hydroxide to a substantially neutral pH, and thereafter mixing with the thus treated fibers in suspension a latex of a synthetic rubber to form a papermaking slurry of rubber-coated fibers, the step of improving the drainage rate of said slurry by adding finely divided zinc oxide thereto subsequent to the addition of said ammonium hydroxide and prior to the addition of said synthetic rubber latex.

2. A process according to claim 1 wherein said zinc oxide is added in an amount of about 350% by weight based on the dry weight of said synthetic rubber.

3. A process according to claim 1 wherein said zinc oxide is added in the form of a dispersion.

4. A water-laid fibrous sheet comprising cellulosic fibers having an inner coating of zinc oxide and an outer coating of a synthetic rubber containing zinc oxide dispersed therethrough.

5. A sheet according to claim 4 containing zinc oxide in an amount of about 3-50% by weight based on the dry weight of said rubber.

6. A sheet according to claim 4 wherein said synthetic rubber comprises a butadiene-styrene copolymer.

7. A sheet according to claim 4 wherein said synthetic rubber comprises a butadiene-acrylonitrile copolymer.

8. A sheet according to claim 4 wherein said synthetic rubber comprises a polychloroprene.

9. A sheet according to claim 4 wherein said synthetic rubber is present in an amount of about 10-100% by weight based on the dry weight of said fibers.

References Cited in the file of this patent UNITED STATES PATENTS 1,947,104 Plumstead Feb. 13, 1934 2,375,245 Pretzel May 8, 1945 2,666,699 McQuiston et a1 Jan. 19, 1954 2,930,106 Wrotnowski Mar. 29, 1960 

1. IN THE PROCESS OF PRODUCING FELTED FIBER PRODUCTS BY SUSPENDING FIBERS IN A SOLUTION CONTAINING THE DISSOLVED SALT OF THE METAL OF THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM, AND ZINC, MIXING WITH SAID SOLUTION AND THE FIBERS SUSPENDED THEREIN AN AQUEOUS SOLUTION OF AMMONIUM HYDROXIDE TO A SUBSTANTIALLY NEUTRAL PH, AND THEREAFTER MIXING WITH THE THUS TREATED FIBERS IN SUSPENSION A LATEX OF A SYNTHETIC RUBBER TO FORM A PAPERMAKING SLURRY OF RUBBER-COATED FIBERS, THE STEP OF IMPROVING THE DRAINAGE RATE OF SAID SLURRY BY ADDING FINELY DIVIDED ZINC OXIDE THERETO SUBSEQUENT TO THE ADDITION OF SAID AMMONIUM HYDROXIDE AND PRIOR TO THE ADDITION OF SAID SYNTHETIC RUBBER LATEX. 